There have been several attempts to make the waveguide grating router (WGR) on InP polarization insensitive. An InP-based router is desired so that it may be implemented along with photodetectors, optical amplifiers, modulators, switches and any other active optoelectronic components on a common InP substrate. The polarization sensitivity is caused by the birefringence of the InP-based waveguides and is a serious problem if the router is used in a receiver or as a passive demultiplexer. This problem can be solved by simply matching the free spectral range (FSR) and electrical field (TE) and magnetic field (TM) shift of the router, but by doing so, one severely restricts the optical bandwidth over which the router can operate. Such an arrangement is described in the article by M. Zirngibl et al. entitled "Polarisation independent 8.times.8 waveguide grating multiplexer on InP," Electronic Letters, Vol. 29, 1993, pages 201-202. Another approach is to make the InP waveguides non-birefringent, as described in the article by B. H. Verbeek et al. entitled "Large Bandwidth Polarisation Independent and Compact 8 Channel PHASAR Demultiplexer/Filter," OFC '94, February 1994, paper PD 13-1. These waveguides, however, do not seem practical for integration with optical amplifiers, for instance. Another technique, described in U.S. Pat. No. 5,341,444 issued to C. H. Henry et al. on Aug. 23, 1994 and entitled "Polarization Compensated Integrated Optical Filters and Multiplexers," has been successfully employed for SiO.sub.2 -based circuits but is not suited for InP-based devices. Thus it is a continuing problem to implement an InP-based router which is polarization independent.